1. Field of the Invention
The present invention relates to a camera, and more specifically it relates to a camera capable of minimizing blurring during a flash photographing operation accompanied by light emission by an electronic flash unit.
2. Description of the Related Art
In a camera that automatically switches to flash photographing if the field brightness is lower than a predetermined brightness level (hereafter in this specification referred to as a "low-brightness auto-flash camera"), the shutter speed in the range of one tenth to one hundredth of a second is normally set for flash photographing. The length of flash time by the electronic flash unit in such a camera is several milliseconds at the most, and the upper limit of the synchronization speed at which the light emission by the electronic flash unit can be made to synchronize with the shutter open/close operation is in the range of one hundredth to one thousandth of a second.
One of the objectives to be achieved by setting the shutter speed for flash photographing lower than the synchronization speed, i.e., at one tenth to one hundredth of a second is an improvement in the depiction of the background. In a hypothetical situation in which a person is photographed against a background of sunset colors after the sunset, a correct exposure can be achieved with respect to the person based upon the aperture set at the camera and the flash amount of the electronic flash unit normally regardless of a shutter speed.
The exposure of the background, on the other hand, which is beyond the range of the flash light, depends upon the aperture and shutter speed set at the camera and the brightness of the background. If the shutter speed is set at the synchronization speed explained earlier, a sufficient exposure quantity may not be achieved depending upon the background brightness and in that case, the background in the finished photograph will be underexposed and become dark and the intended depiction results will not be obtained. This is not a problem that occurs only when the sunset color is used as the background but is a common problem which may occur any time the distance between the main subject and the background is so great that the light from the electronic flash unit cannot reach the background and the brightness of the background is relatively low.
In addition, since the illuminating light is irradiated on the subject almost directly from the front in a flash photographing operation performed with a camera internally or externally mounted with an electronic flash unit, if the subject is a person, the subject's face may look devoid of shade and depth, which will result in an unnatural look.
In order to address the problems explained above, the shutter speed for flash photographing is often set relatively low in a low-brightness auto-flash camera. In other words, by performing a photographing operation using ambient light and not emitting light from the electronic flash unit unless the field brightness reaches a predetermined lower limit at which the required shutter speed is too low and would result in noticeable hand-movement blurring (caused by camera vibration by hand tremble), photographing results that reflect the ambience of the location can be obtained. The ambient light means light in case that the electronic flash unit is not used.
Then, flash photographing is performed when the field brightness becomes lower than the brightness limit at which hand-movement blurring becomes a problem as described above. The flash photographing operation is performed by fixing the shutter speed at a specific value, i.e., at the shutter speed with flash operation, even when the field brightness becomes low. By lowering the brightness level at which the camera is switched from ambient light photographing to flash photographing as much as possible and lowering the shutter speed with flash operation, flash photographing results with superior background depiction can be obtained with greater ease.
However, if the brightness level at which the camera is switched from ambient light photographing to flash photographing is set low and the shutter speed for flash photographing is also set relatively low as described above, a problem arises of the background becoming blurred easily as explained below.
While the shutter speed for flash photographing is set by ensuring that hand-movement blurring is minimized, it needs to be set relatively low in order to achieve an improvement in the background depiction. In addition, the shutter speed at which hand-movement blurring becomes noticeable varies depending upon individual photographer's skills, the way the camera is held, the manner in which the shutter release button is pressed and the like.
Thus, while the main subject can be photographed with clarity by taking advantage of the stop-action effect achieved by a very short flash duration at the electronic flash unit, the background sometimes becomes blurred and unacceptable. In particular, the quality of an image photographed with objects having a relatively high brightness level such as street lamps or neon signs as points of light in the background, for instance, may become even worse due to leaving tails of the street lamps or neon signs.